The expanse of communications networks has grown from the public switched telephone network ("PSTN") to include many different types of networks. For instance, wireless communications networks have grown in popularity such that it is not uncommon for mobile switching centers (MSCs) to have service requests numbering in excess of 100,000 call attempts per hour in a single metropolitan area. In these metropolitan areas, each MSC may serve a network of 100 or more cell sites, or base stations, each of which defining a particular cell.
On occasion, it is important to trace an in-coming call to a land-line telephone or a wireless telephone. The PSTN has systems in place today perform traces for calls terminating to a land-line telephone. However, the systems used for tracing calls terminating to land-line telephones does not work for those terminating to wireless telephones. This is true regardless of whether the caller is using a mobile unit or a land-line device.
The difficulty in tracing calls that terminate to a wireless telephone are inherent with the very nature of wireless communication networks, e.g., the absence of hard, physical links between the MSC and a mobile unit, such as a cellular telephone. In wireless communication networks, the mobile unit subscribes to a particular network of MSCs and the subscribed network maintains a record for the wireless unit in a home location register ("HLR") database. The record includes information such as a home location for the mobile unit, subscribed capabilities such as call waiting or call forwarding, and current status (e.g., active or inactive). The mobile unit may roam, or visit, in many different MSCs that have a signaling link to the HLR. Therefore, each MSC also keeps track of visiting mobile units currently operating in its service area via a database commonly referred to as a visitor location register (VLR). The VLR contains information regarding the services available to each visitor, his subscribed network, his HLR, and his current status.
When an in-coming call attempts to connect to a mobile unit, it first contacts an originating MSC of the mobile units subscribed network. The originating MSC queries the HLR for the mobile unit's location. If the mobile unit is in the area served by the originating MSC, the originating MSC establishes communication with the mobile unit and services the call. If the mobile unit is not in the area, additional MSCs and their associated VLRs must be contacted in order to locate the mobile unit and establish connection.
Presently, the only method for tracing a call terminating in a wireless telephone network is through a service like caller-ID. If the caller allows, caller-ID receives the calling party number ("CPN") for use by the called party. However, caller-ID can be avoided or inhibited by some callers and is not available from other callers, thereby reducing or eliminating its usefulness for tracing. Furthermore, the information from caller-ID is limited in that only the CPN is provided, and is therefore only partially useful.
Therefore, what is needed is a system that can trace all calls, providing as much information as possible.